BMW Repair: 520d 09 - air circulation problem, circulation problem, vacuum lines

Question
need help... periodically, smoke from the outside gets in to the car even if the air circulation button is on... the A/c is not in auto mode... dealer says that it is normal as the system is programmed to introduce air from the outside every so often to introduce "fresh" oxygen... is this true? i don't want this, carbon monoxide is not welcome inside the car.... pls help on how to fix this


Answer
I have to assume this is a diesel,being it is written as a 520d.The dealer is correct at some point as the air is allowed to come in but it is filtered.Have you ever had the cabin filter replaced?And the circulation doors should be checked to make sure they are working as they should.The engine,although being diesel, shouldn't smoke that much and if it does being an 09 warrantee must cover some of it.The smell must be smoke or is it a diesel fuel smell?There are many vacuum lines  to canisters,possibly a cracked unit?One good thing ,its not carbon monoxide(CO) you are smelling,it is odorless.